The Tech L33T

Custom “Virtual Network Operator” Role in Azure

Posted on June 25, 2019 Updated on June 9, 2020

Reading Time: 4 minutes

*Edit* 6/9/20: At the time of writing this blog custom roles were not available in the Azure Portal. Since that feature now exists, I’ve added how to create this role through the portal to the end of this blog.

We all know that cloud environments are different than on premises. Development environments can be even more difficult, the right cross between giving freedom to produce business value and enough security and controls to maintain a good security posture. Recently I came across a scenario where the design was that the networking components (Virtual Network, S2S VPN, Peerings, Service Endpoints, UDRs, Subnets, etc.) were all under the control of a Networking team so that the Azure environment would be an extension of their local network. From a permissions standpoint though this caused some problems. The goal would be to empower developers to build whatever they need and just attach it to the vNet when connectivity was needed, with the caveat that they shouldn’t be able to modify any of the network settings or configurations in the shared vNet. This however, turned out not to be possible with default IAM roles.

In my testing, even though you’re not “modifying” anything per se in the vNet – when attaching a network interface card to a Subnet it does require write access. Reader access will give the user this error.

After looking through the default IAM roles, there aren’t any that do what I need them to do. Alas, a custom role is needed. For reference, please checkout this docs page for custom roles – https://docs.microsoft.com/en-us/azure/role-based-access-control/custom-roles.

First, I need to see what actions are available to pack into the custom role so I run the following command in Azure Powershell and get these results.

Get-AzProviderOperation “Microsoft.Network/virtualNetworks/*” | FT OperationName, Operation, Description -AutoSize

Great, now I can see what is available. It looks like the actions that I need are the /subnet/join/action and /subnet/joinViaServiceEndpoint/Action. Based on the descriptions these two will essentially give “operator” role to the vnet. The assignee will be able to use the subnet(s) but not able to modify them.

Next, you can use one of the template references in the Microsoft Docs link (https://docs.microsoft.com/en-us/azure/role-based-access-control/custom-roles-powershell#create-a-custom-role-with-json-template) and modify the actions.

{
  “Name”: “Custom – Network Operator Role”,
  “Id”: null,
  “IsCustom”: true,
  “Description”: “Allows for read access to Azure network and join actions for service endpoints and subnets.”,
  “Actions”: [
  “Microsoft.Network/virtualNetworks/subnets/join/action”,
  “Microsoft.Network/virtualNetworks/subnets/joinViaServiceEndpoint/action”,
  “Microsoft.Network/virtualNetworks/read”
   ],
  “NotActions”: [],
  “AssignableScopes”: [
  “/subscriptions/00000000-0000-0000-0000-000000000000”,
  “/subscriptions/11111111-1111-1111-1111-111111111111”
  ]
}

After modifying the assignable subscription IDs, save that as a .json file and use it in the following command to import the custom role.

New-AzRoleDefinition -InputFile “C:\FileFolderLocationPath\CustomNetworkOperatorRole.json”

After a portal refresh you get the custom role available as an IAM role assignment.

There you go, after assigning this role the user was able to create VMs and attach them to the Virtual Network while still leaving control of the Network configuration to the Networking Team.

————————————————————————-

————————————————————————-

EDIT 6/9/20: Now that custom roles are available in the portal I’ve added how to create this role that way below. 

Using the documentation on how to create custom IAM roles in the Azure portal you can clone any role, but I’m just going to use the “Network Contributor” role to clone. 

I am going to just “start from scratch”, though you can easily use this page to modify the permissions set of a certain role that already exists. Additionally, if you have the JSON (like we generated before with powershell) you can just upload that here.

Now go ahead and add new permissions by going to the “Microsoft Network” Category and selecting the same permissions we wrote in the JSON and used with the powershell command above.

After adding those the next page will show you the permission that you’ve added, let’s double check those and make sure we have what we need.

Looks good, now we can set a scope where this role can be applied. I have this one scoped to the whole subscription, but you can use the interface to easily change that on this page.

Alright, that’s about it – let’s take a quick look at the summary pages. You can see that the portal actually generates the JSON, which is nice if you want to assign roles using Azure Policy or any other automation tooling.

Nice! Now we can see that users can use the four above actions which will allow them to interact with, and use a shared hub-style virtual network while now allowing full contributor access.

I hope I’ve made your day at least a little bit easier!

If you have any questions or suggestions for future blog posts feel free to comment below, or reach out to me via email, twitter, or LinkedIn.

Thanks!